1. Field of the Invention
The invention relates to a circuit board, and more particularly, to a through-hole layout structure suitable for a circuit board and used to reduce signal interference, and a circuit board and an electronic assembly adopting the through-hole layout structure.
2. Description of Related Art
The application of the current Universal Serial Bus 3.0 (USB 3.0) is widely used. However, issues of electromagnetic interference (EMI)/radio frequency interference (RFI) may occur at a frequency of about 2.5 GHz. The reason is, USB 3.0 has a data rate of 5 Gbps and the clock frequency thereof is 2.5 GHz. Therefore, an apparatus (such as the wireless module of a wireless mouse) at an operating frequency of about 2.5 GHz may fail due to interference from the signal on an USB 3.0.
For instance, the hub of USB 3.0 has a circuit board and a USB 3.0 chip and a USB 3.0 electrical connector installed on the circuit board. When a plastic material is adopted for the casing of the hub of the USB 3.0 and a suitable metal shield is absent, the RFI emitted by the USB 3.0 signal (clock frequency of 2.5 GHz) transmitted by the circuit board is about 2.5 GHz. Such EMI/RFI may affect the wireless module of a wireless mouse at an operating frequency of 2.4 GHz.
A method of differential signal is adopted for the architecture on an USB 3.0 for signal transmission. A differential transmission path needs to have good symmetry to ensure balance of the differential signal. When the differential transmission path is asymmetric, the differential signal may be converted to an undesired common mode noise, thereby causing the issue of RFI.